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Why a known device may later become unrecognised

As privacy became a greater concern for users of mobile devices such as iPhones, iPads and Android phones, operating systems introduced the random MAC-address feature. This enhancement boosts user privacy, but it also complicates device recognition.

The Media Access Control (MAC) address is a unique identifier assigned to a device. Traditionally, this address remained static, enabling networks and network tools like WiFi Guard to identify such devices consistently. However, in recent years operating systems implemented MAC-address randomisation, which obscures network identity of devices. Depending on their settings, devices can periodically change their MAC-addresses, especially when connecting to new Wi-Fi networks.

Network monitoring tools, such as WiFi Guard, rely on MAC-addresses for identifying devices. When a user marks a device as known, WiFi Guard associates the discovered MAC-address with the device status. If the device later changes its MAC-address, WiFi Guard will correctly detect the new MAC-address, but will not associate it with the same device until the user tells WiFi Guard that this is indeed the same device. This is an unavoidable trade-off between security and convenience.

To make your experience more streamlined, you can choose to use fixed MAC-addresses for your trusted networks, such as your home network. In this case, the device will use the same MAC-address in that particular network, and WiFi Guard will identify it correctly each time.

MAC-address options in various devices

Apple devices (macOS, iOS, iPadOS)

Open Settings, then Wi-Fi, and then tap the “i” or “…” icon next to the name of your Wi-Fi network to access its settings.
Scroll down to Private Wi-Fi Address and select the option that is best for your situation:
- Off: the device will use its real, static hardware MAC-address. This option provides the lowest level of privacy, because the device can be easily recognised and tracked. Not recommended, unless you trust your surrounding Wi-Fi networks and devices.
- Fixed: the device will use a unique address for this network, allowing reliable device recognition within the network, but reducing cross-network tracking. This is a balanced option for privacy that also offers reliable detection by WiFi Guard.
- Rotating: the device will periodically change its address on this network. This option offers the best privacy, but each time the device changes its address, WiFi Guard will detect it as unrecognised.

Windows devices

Open Settings, then go to Network & Internet, and click on Wi-Fi.
Select Manage Known Networks.
Choose a network, click Properties, and select one of the following options under Random Hardware Addresses:
- On: the device will use a random MAC-address when connecting to new networks. Random hardware addresses are typically enabled by default for all public networks, but can be turned off for specific networks if you trust them.
- Off: the device will use its real MAC-address. This can be a suitable option for the trusted home or corporate networks.

Android devices

Open Settings, then tap Network & Internet or Connections, depending on your device.
Select Wi-Fi.
Tap the gear icon or info icon next to the connected network, or long-press the network name.
Select one of the following Privacy options:
- Use Randomised MAC: the device will use a random MAC-address for the network. Latest Android versions enable randomised MAC-addresses by default for new networks.
- Use Device MAC: the device will use its hardware MAC-address for the network, ensuring consistent identification but with lesser privacy.

Other devices

Some devices like smart TVs and gaming consoles also support MAC-address randomisation, but the process varies by brand. Generally, these settings can be accessed via Network Settings or Wi-Fi Settings. Look for options like “MAC Randomisation” or “Private Address”.